Projects
Introduction
Convergent plate margins and subduction zones as a result of dynamic lithospheric plates are first order features shaping the Earth. Convergent continental margins combine the majority of processes affecting the internal architecture, thermal, and geochemical character of continental lithosphere. In addition, the close relations between convergent plate margins, active deformation and uplift, magmatism and associated crustal growth, as well as more than 90% of global seismic energy release make these plate boundaries important natural laboratories where mass and energy flux rates can be studied at various scales. Since the advent of plate tectonic theory, it has been recognized that all of these phenomena are intimately related and often governed by feedback mechanisms. Accordingly, subduction orogeny has become an international high priority theme in process-oriented earth-system analysis. Consequently, the complex interactions of subduction orogeny represent the principal motivation to define and initiate our research program on the Andes.
Since the integration of the concepts of orogeny into the plate tectonic framework, the Andes have been considered as the type example of a subduction-related orogen. As such, the Andes contrast with collision-related orogenic belts of the Alpine-Himalayan type. While the fundamental differences between these two orogenic end members and their salient features are well established and undisputed, the mechanisms and processes driving them, however, are a matter of continued international debate. During the past decade, this debate has grown in intensity along with a major increase in multidisciplinary international research programs in both settings. To further define and refine our knowledge of subduction orogeny the Andes are an excellent site. In fact, the Andes are the Earth's largest active subduction-controlled orogen. Cenozoic mountain building in the Andes has been controlled by long-term subduction of several oceanic plates without collisional overprint, active arc magmatism in most segments of the overriding plate, and substantial continental thickening. In addition, the northernmost and southermost parts of the Andean orogenic system exhibit other convergence parameters and styles of orogeny as compared to the central parts. The Andes also encompass the second largest orogenic plateau on earth with similarities to the Cenozoic Tibetan Plateau. Finally, recent advances in the understanding of feedback mechanisms between climate and tectonics in other convergent margin settings have demonstrated the role of meridianally trending orogens with respect to prevailing latitudinal wind and precipitation patterns. Latitudinal climatic variations stored in the rock record along the Andes thus record the evolution of climate in South America as well as its interaction with continued uplift.
In summary, the Andean plate margin offers a rich spectrum of research opportunities which will improve our understanding of fundamental not only differences, but also similarities between subduction and collision orogeny. No other subduction orogen shows such large systematic changes of several plate kinematic boundary conditions as well as differing climatic constraints along strike. The Andes can thus be considered a global site for a systematic study of the interaction of parameters and processes in subduction orogeny and related surface processes.
Since early 1993, members of the collaborative research program 267 - 'Deformation processes in the Andes' - have been actively working on establishing a broad scientific basis covering a variety of features in the Central Andes. Following the first half of the planned 12-year program, the emphasis of the scientific program was changed. This was mainly determined by a growing body of data and evidence, and by a major turnover of scientific personnel due to retirement. The first two funding periods were devoted to collecting a vast, mainly geophysical and geodetic data base, complemented by studies on the geological evolution of the Central Andean region during the Phanerozoic. The results formed a basis to define more precisely the aim for the second half, specifically improving our understanding of the mutual relationship between internal and external mechanisms in Cenozoic deformation and plateau building. This change in strategy is a natural consequence toward the final stage of a process-oriented research program. Starting in the present phase, earlier work has been complemented by an increase of experimental research and by field-based studies which focus on key aspects of expected relevance to derive process-oriented information from the rock record. Also, we have included a second study area in the North Patagonian Andes which, due to its different architecture and evolution, is considered an ideal setting to test models and assumptions on subduction orogeny developed from Central Andean data.
The concept described below for the next funding period is a logical continuation of this strategy. Accordingly, research will continue to focus on two main study areas, one in the Central Andes in Northern Chile/southern Bolivia/northern Argentina, where formation of a non-collisional plateau has played the dominant role, and the second in southern Chile/Argentina where a more 'standard type' of continental subduction orogen without plateau formation has developed in spite of similar plate kinematic boundary conditions. In addition, the forthcoming stage will emphasize simulation and modelling of processes expected to be of paramount importance in creating a subduction orogen and causing plateau formation. Complementary field-based projects in the above named areas will fill in additional key data that are of crucial interest to test conflicting hypotheses and to complete a process-oriented understanding of the orogen.
This development of our research program is fostered by the development of personnel in the four participating institutions. Following the major change of senior research staff and the inclusion of a large number of new members from the participating institutions, the active expertise in interpretation-related and modelling studies has been strengthened substantially, a basic requirement for the described development of the program. In accordance with the personnel change and the main results of the present phase (see chapter on key results) we have also reshaped the internal structure of our program. From the three presently active research themes (plus one technical research themes), we have developed our plans to focus on two major groups of processes that are linked to two of the major components of a subduction orogen which are also the focus of international discussion. The research themes are:
- Deformation and Forces at a Convergent Plate Margin
- Mechanisms of Plateau Formation
- Central tasks
We have defined 12 sub-projects in these programs. Within this structure, we plan to synthesize and complement our current results with a strong bias towards modelling-oriented studies and associated field-based studies that will both systematically test and refine hypotheses and ideas on plateau formation and subduction orogeny.